Method of producing an acoustical tile



Dec. 7, 1965 c. E. STEDMAJJ 3,222,434

METHOD OF PRODUCING AN AC USTIGAL TILE Original Filed Jan. 26, 1959 '7Sheets-Sheet 1 FIE.5

INVENTOR. CRESSWELL E. STEDMAN, deceased, By ELIZABETH K. STEDMAN,

ADMINISTRATRIX,

BY A-r'r V.

c. E. STEDMAN 3,222,434

METHOD OF PRODUCING AN ACOUSTICAL TILE 7 Sheets-Sheet 2 INVENTOR.CRESSWELL E. STEDMAN,deceused, ELIZABETH K. STEDMAN BY ADMINISTRATRIZQDec. 7, 1965 Original Filed Jan. 26, 1959 Fl 5. E

Dec..7, 1965 c. E. STEDMAN 3,222,434

METHOD OF PRODUCING AN ACOUSTICAL TILE Original Filed Jan. 26, 1959 '7Sheets-Sheet 3 FJ. 13 f1 Q114- f 15 I40 1 1 w a 1 I32 ,436 42 W, 4 MW,49

INVENTOR.

CRESSWELL E. STEDMAN,deceused, By ELIZABETH K. STEDMAN,

ADMINISTRATRIX,

JMQ/ QM Dec. 7, 1965 c. E. STEDMAN METHOD OF PRODUCING AN ACOUSTICALTILE 7 Sheets-Sheet 4 Original Filed Jan. 26, 1959 1955 c. E. STEDMAN 3,

METHOD OF PRODUCING AN ACOUSTICAL TILE Original Filed Jan. 26, 1959 '7Sheets-Sheet 5 CRESSWELL E. STEDMAN, deceased, By ELIZABETH K. STEDMAN,

' ADMINISTRATRIX,

MQM

ATTY.

Dec. 7, 1965 c. E. STEDMAN METHOD OF PRODUCING AN ACOUSTICAL TILE 7SheetsSheet 6 Original Filed Jan. 26, 1959 CRESSWELL E. STEDMAN,deceased, By ELIZABETH K. STEDMAN,

ADMINISTRATRIX, QZMZQJQ W Dec. 7, 1965 c. E. STEDMAN 3,222,434

METHOD OF PRODUCING AN ACOUSTICAL TILE Original Filed Jan. 26, 1959 '7Sheets-Sheet '7 INVENTOR.

CRESSWELL E. STEDMAN, deceased, By ELIZABETH K. STEDMAN,

ADMINISTRATRIX,

United States Patent O 3,222,434 METHOD OF PRODUCING AN ACOUSTICAL TILECresswell E. Stedman, deceased, late of Chicago, 11]., by

Elizabeth K. Stedman, administratrix, Chicago, Ill., assignor to US.Perlite Corporation, Chicago, 111., a corporation of Delaware Originalapplication Jan. 26, 1959, Ser. No. 788,998, now Patent No. 3,103,254,dated Sept. 10, 1963. Divided and this application June 14, 1963, Ser.No. 288,046

1 Claim. (Cl. 26425) This application is a division of co-pendingapplication, Serial No. 788,998, filed January 26, 1959 and which is nowPatent No. 3,103,254 issued September 10, 1963, and which latterapplication is a continuation-inpart of and consolidates applicationsSerial No. 542,321, filed October 24, 1955; Serial No. 614,783, filedOctober 9, 1956; and Serial No. 677,194, filed August 9, 1957 which areall now abandoned.

This invention is directed to a method of making an acoustical tile froma tile-forming composition.

It has been known to employ various materials in the manufacture ofacoustical tile and among these are mineral wools, vermiculite, perlite,asbestos, gypsum and other materials, together with various bindersincluding sodium silicate, but notably starch and other flammableorganics. However, insofar as is apparent, it has not been foundpossible heretofore to make a satisfactory acoustical tile usingasbestos fibers, vermiculite, perlite, and sodium silicate, or likefire-resistant binder, notwithstanding the fact that the porous andother desirable characteristics of vermiculite, perlite, and asbestosfibers have been known to have desirable characteristics for themanufacture of acoustical tile.

It has been ascertained that a primary difiiculty in employingvermiculite, perlite, and asbestos in the manufacture of acousticaltile, with a fire-resistant inorganic mineral binder, such as an aqueoussolution of an alkali metal silicate, such as sodium silicate, has beenthat the sodium silicate binder penetrates the fibers of the asbestosand the pores or interstices of the vermiculite or perlite mineral sothat when the composition is dried the result is an ineffective hardsurface or hard-walled more or less ceramic tile which has littlesound-absorbing elficiency and substantially no utility as acousticaltile, and lacks dimensional stability in that it will absorb water vaporand warp, sag or buckle in use. Moreover, in the prior attempts to usevermiculite and perlite in the manufacture of acoustical tile, employingsodium silicate as a binder, the sodium silicate binder has been foundto be unstable in the use of the tile, due to water-absorption, and forother reasons causing resultant swelling and warpage in the tile. It hasbeen additionally found that one of the principal reasons why perlite orvermiculite has not proven satisfactory in acoustical tile is that theseare ground up and crushed during the later stages of mixing and molding,losing their initial hollow, closed pocket or envelope characteristic,and when in such a fine state lose their acoustical properties.

It has been now found that a highly efiicient and relatively inexpensiveacoustical tile may be manufactured according to the present inventionusing asbestos fibers and vermiculite, or perlite, or equivalentexfoliating or expandable minerals of volcanic origin, and which aresometimes referred to as volcanic glasses, as base materials and usingan alkali metal silicate as a fire-resistant inorganic mineral binderand in such a manner as to overcome the objections and difiicultiesheretofore experienced in attempts to use vermiculite and expandedperlite, and asbestos or equivalent materials, with a sodium silicate or3,222,434 Patented Dec. 7, 1965 equivalent alkali metal silicate binderin the manufacture of acoustical tile.

Accordingly, an object of the present invention is to provide a newimproved method of making an acoustical structural building unit whichis highly efiicient from the standpoint of sound-absorption in the rangeof the sounds of normal human speech and hearing, and also in the rangeof low-pitched sounds, and which is particularly desirable for use inand upon the ceilings and walls of buildings where the problem ofsound-absorption in the range of the sounds of normal human speech andhearing, and in the range of low-pitched sounds, is encountered. Anotherobject is to achieve a fire proof acoustical tile containing nocombustibles and composed entirely of mineral or inorganic materials andhence highly heat insulating.

Another object of the invention is to provide a new and improved methodof making an acoustical tile unit in which the asbestos fiber and thevermiculite and/or expanded perlite, or equivalent material, as themineral components thereof, are so treated that the porous,soundabsorbing characteristics and other desirable properties of bothmaterials are retained while, at the same time, these materials, and theother materials employed therewith, are formed into an acoustical tilewhich has a high coeflicient of sound-absorption, and the necessarystability or freedom from swelling and warpage or buckling or otherdimensional changes, and which may be cemented,-

nailed or otherwise fastened upon the ceilings and walls of variousbuilding structures.

Further objects of the present invention are to provide a new andimproved method for making the new acoustical tile, and to protect thevermiculite or perlite particles against crushing. I

An additional object of the invention is to provide a new and improvedmethod for making the new acoustical tile which may be made in varioussizes and which may be cemented, nailed or otherwise fastened to aceiling or wall surface without excessive abnormal fracturing orchipping or like damage during or as a result of normal or conventionalfastening operations.

A further object of the invention is to provide a method of making areinforced acoustical tile unit in the form of an acoustical tile boardwhich may be made not only in the form of ceiling and wall tile ofconventional sizes but also in relatively larger sizes such, forexamplefas slabs or panels two feet square, and which may be readilycemented, nailed, or otherwise fastened to or suspended from a ceilingor wall surface without warping, buckling, fracturing, chipping orsagging.

Other objects will appear hereinafter.

FIG. 1 is a plan view of an acoustical tile embodying a typical form ofthe present invention;

FIG. 2 is a transverse sectional view thereof on lin 22 in FIG. 1; 3

FIG. 3 is a plan view of another embodiment of the invention;

FIG. 4 is a sectional view on the line 4-4 of FIG. 3;

FIG. 5 is a plan view of another embodiment of the FIG. 10 is a showingbased on microscope studies of the nature of the composite bodies makingup acoustical tile of the present invention;

FIG. 10A is a showing of another form of composite bodies making upacoustical tile of the present invention;

FIG. 11 is a schematized perspective view of certain equipment used inthe manufacture of tile under the present invention;

FIG. 11A shows different states of the material undergoing preliminarydensification;

FIG. 12 is a perspective view on an enlarged scale in comparison to FIG.11 and illustrating details of equipment at the mold loading station;

FIG. 13 is a perspective view of a mold tray;

FIG. 14 is a top plan view of the mold tray shown in FIG. 13;

FIG. 15 is a perspective view of a pallet screen used under the presentinvention;

FIG. 16 is a schematized perspective view illustrating further detailsof processing equipment used in practicing the present invention;

FIG. 17 is another schematized perspective view illustrating stillfurther details of equipment used in practicing the Present invention;

FIG. 18 is a perspective view of an acoustical tile produced under thepresent invention;

FIG. 19 is a bottom plan view of the tile shown in FIG. 18;

FIG. 19A is a sectional view taken on the line 19A-19A of FIG. 19;

FIG. 20 is a perspective View of equipment used in the kerfing station;and

FIG. 21 is a fragmentary sectional view illustrating the manner in whichtwo tiles under the present invention are to be suspended from aceiling.

A typical embodiment of an acoustical structural building unit in theform of an acoustical tile made in accordance with the presenceinvention is illustrated in FIGS. 1 and 2 of the drawings, where it isgenerally indicated at 10, and comprises a body 11 of suitable size,shape and thickness, which may have a molded beveled edge 12, and isadapted to be cemented, or otherwise fastened, or suspended, in anysuitable manner, upon the ceiling or wall of a building such, forexample, as an office, restaurant, hotel, auditorium, or the like, wherethe problem of deadeuing sound in the range of the sounds of normalhuman speech and hearing, and also in the range of low-pitched sounds,is encountered.

A preferred composition which may be employed in making the acousticaltile illustrated in FIGS. 1 and 2 is illustrated in and by the followingexample:

Example N 0. 1

To produce an acoustical tile in accordance with the practice of thepresent invention, and which is /8" thick by 12 x 12" square, 12.5 oz.of No. 3 vermiculite particles, known as the so-called Industrial gradeAmerican Standard and 3 oz. of No. 7D04 asbestos fibers (CanadianStandard) are thoroughly mixed. The particle size of the vermiculitereferred to above should be in the intermediate mesh size or range of16-30-50, as more particularly referred to hereinafter. During themixing operation the small plates or platelets of vermiculite and theabestos fibers adhere to each other such that the asbestos fibers whenpermanently adhered to the particles of vermiculite, as will beexplained, form composite bodies in which the asbestos fibers form aprotective pile array about the out side of the particles preserving thehollow body or initial particle construction which has highlyadvantageous acoustical properties.

The mixture thus formed is then sprayed, preferably by means of a spraygun, or the like, with a fine spray of a fire-resistant andwater-repellent coating composition such, for example, as an organicwater-soluble so-called silicone resin, and for this purpose it has beenfound th t a 4. called organic water-soluble silicone resin known as DowCorning No. XS1 is very satisfactory, this material being a watersolution of sodium salts of organosilanols and organosiloxanols. Thiscoating composition represents the first inner coating surface and bondsthe asbestos fibers in place on the outside of the vermiculiteparticles, forming composite bodies wherein the vermiculite (or perlite)particles are insulated one from another so as not to grind one on theother during further mixing and molding. These bodies are shown in FIG.10 as microscope representations wherein the vermiculite (or perlite)particle P are surrounded by abestos fibers A in intimate bonded contact therewith. The mixing operation is continued during this sprayingoperation forming more and more of the composite bodies and until themixture becomes somewhat darker in color and all of the asbestos fibersand the vermiculite particles have been well coated and renderedwater-resistant or water-repellent by the silicone resin material. Themixture thus formed is then heated to a temperature of 150 F., and ismaintained at this temperature for a period of about fifteen minutes,and until it is thoroughly dried, this drying temperature being capableof being varied from F. to F. for the time stated, whereupon the mixtureis again mixed or agitated until it assumes the form of a light fiuffymass.

A binder in the form of an aqueous solution of sodium silicate is thenthoroughly mixed with the composition prepared as above to provide thenext outer coating surface on the bodies, and for this purpose it hasbeen found that for the quantities of vermiculite and asbestos indicatedabove, from 24 to 28 02., with an optimum of 26 oz., of an aqueoussolution of sodium silicate, known as the so-called No. 40 (DiamondAlkali Company) sodium silicate, is very satisfactory, this materialhaving a specific gravity of 40.0041.5 B. 1.38-1.40 with an averagesolids content of 37.5 percent. This mixing operation is continued for aperiod of about five minutes whereupon the com position assumes a goldenbrown color.

The mold is then filled with the asbestos-vermiculite composite bodies,prepared and treated as above, and the thus filled mold is thencompressed to a thickness of M2, whereupon the thus formed acousticaltile shape can be placed in a drying oven on a fiat metal pallet andthoroughly dried at a temperature of preferably not in excess of 200 F.for a period of from 6 to 8 hours, after which it is allowed to coolgradually to room temperature in the drying oven. This procedure hasbeen found to be effective in preventing warping of the tile and inproducing a uniformly fiat acoustical tile, and during consolidation ofthe mass of composite bodies the asbestos pile surface on the particlesP, FIG. 10, preserves and maintains the original formation of theparticles P and maintains some spacing between the particles P in thefinal product thereby affording many voids permitting sound to penetratethe consolidated acoustical tile product.

After the resulting tile form or shape has been thus dried and allowedto cool it has been found, in one mode of practice of the presentinvention, and to produce stability and resistance to moistureabsorption in the binder and freedom from warpage and buckling in thenew tile, it should be treated with a three percent aqueous solution ofmagnesium silico-fluoride (magnesium fiuosilicate), which may be appliedin any suitable manner, as by spraying, at an air pressure of 60 lbs.,so as to thoroughly impregnate the entire mass including the sodiumsilicate binder. The exact nature of the action of the magnesiumsilico-fiuoride (magnesium fiuosilicate) on the composition is not knownbut it is believed to react at least partially with the sodium silicatebinder to provide a binder material which is highly stable and resistantto absorption of moisture or water vapor while, at the same time,eliminating the hard, glossy outer surface formed on the tile shape bythe sodium silicate binder and providing an outer surface on the newacoustical tile shapes which is of a soft, porous texture and has goodacoustical properties. The new tile form or shape may then also, ifdesired, be provided with a suitable-colored surface coating such,

\ for example, as a water-soluble casein paint of any desired color, orthe like, to impart any desired color thereto.

In making the new acoustical tile in accordance with the foregoingExample No. 1, and in the dimensions stated, and in the particle sizehereinafter referred to, the amount of the vermiculite employed shouldnot be less than oz. nor more than 14 02., since if the amount ofvermiculite is less than 10 oz. the resulting tile will be too fragileand if it is more than 14 02., the resulting tile will be too dense.

It has been found that the new acoustical tile embodying the compositionand made in accordance with the method set forth above is a highlyeflicient fire-resistant, structurally strong and stable, and thoroughlywater-re pellent and water vapor-repellent acoustical tile having a highcoefficient of sound absorption at both the low frequencies and the highfrequencies at which sound absorption coefiicients are customarilyspecified.

It has been further found that by providing the mixture of asbestos andvermiculite (or perlite as will be explained) with a water-repellentcoating prior to the time the binder in the form of an aqueous solutionof sodium silicate is incorporated therewith, a greatly improvedacoustical tile is afforded. This action or phenomenon is believedpartly due to the fact that when the asbestosvermiculite orasbestos-perlite composite body base is thus treated with thewater-repellent composition, the sodium silicate binder is preventedfrom penetrating into and filling up the pores and interstices in thevermiculite and in the asbestos fibers so that the naturally occurringand inherent voids in these materials are left open and unfilled andserve, in the finished acoustical tile, to provide soundabsorb-ing areasor interstices, and thus enhance the sound-absorbing and sound-deadeningefficiency of the resulting product.

It is now apparent, however, that the major effect is due to the securedor bonded pile effect of the asbestos about the acoustical vermiculite(or perlite) particles. These particles are originally hollow or ofclosed pocket or envelope, highly fragile form. If safeguarded againstgrinding contact one on the other, as is accomplished by the asbestospile surface, the original form is maintained and there is spacingbetween the particles in the final product. The hollow nature isparticularly so where the particles are of the expanded type, but evenif perchance hollow particles are not always present, the asbestos pilelayer prevents rupture of the fragile particles during mixing andpressing, thereby maintaining the original particle size, and assuresspacing between the composite bodies in the final consolidated tileproduct.

At the same time, the new acoustical tile is rendered thoroughlywater-repellent and water vapor-repellent and fire resistant and highlystable by treatment in the manner set forth in the foregoing Example No.1 by treatment with the aforesaid organic silicone resin and with themagnesium silico-fluoride composition, without interfering with thedesired acoustical characteristics of the finished tile.

By the term vermiculite, as used herein is meant the naturally occurringmicaceous mineral of this name which is chemically a hydrated magnesiumsilicate of somewhat indefinite and variable but characteristiccomposition found in Montana and North Carolina, and perhaps elsewhere,and which when expanded by heat to about 2000 F. forms a refractoryproduct which is highly resistant to fusing under high temperatures(Condensed Chemical Dictionary, Fourth Edition (1950), ReinholdPublishing Corp., page 693). Also included within the term ofvermiculite, as herein used, are certain commercial forms of vermiculitewhich are, mineralogically, hydrobiotites.

Example N0. 2

As a modification of the procedure set forth in the foregoing ExampleNo. 1, one may place in the mold a 6. quantity of theasbestos-vermiculite composite body mixture (treated with thewater-soluble silicone resin and sodium silicate binder) sufficient tofill the mold only approximately half full and then spread over thesurface of the material in the half-filled mold a relatively thin layerof the asbestos-vermiculite composite body mixture which has beentreated with the water-repellent silicone resin but not with the sodiumsilicate binder. For this purpose one-half /2) ounce of theasbestos-vermiculite composite body mixture treated with thewater-repellent silicone resin is sufficient. The mold may then becompletely filled with the asbestos-vermiculite mixture treated with thewater repellent silicone resin and sodium silicate binder, and theoperation of forming the new acoustical tile completed in the manner setforth in the foregoing Example No. 1.

It has been found that the new acoustical tile, made in accordance withthe practice set forth in the foregoing Example No. 2, enhances thesound-absorbing characteristics of the new acoustical tile by affordinga mass of air spaces in the middle body portion of the tile which is ofparticular advantage in those instances in which it is contemplated thatthe new acoustical tile will be used without an auxiliary air spacebehind it where it is planned to rely for sound-absorption entirely onthe sound-absorption characteristics of the new acoustical tile itselfand an acoustical tile of high sound absorption and sound-deadeningcharacteristics, is, therefore, desired.

Example N0. 3

In this example the same procedure and steps may be followed as areemployed in either of the foregoing Examples Nos. 1 and 2 except that 15oz. of so-called grade No. 3 vermiculite and 3 oz. of asbestos of theso-called grade No. 7D04 may be employed in preparing an acoustical tile12 x 12 in size and Vs thick.

Example N0. 4

In place of the aqueous solution of magnesium silicofiuoride, MgSiF -6HO, referred to in the foregoing Example No. 1, one may employ as asubstitute therefor an aqueous solution of ammonium silicofiuoride(ammonium fluosilica-te), (NH 2SiF and for this purpose one may employ aone percent aqueous solution of the same ammonium silicofluoride,according to the same procedure set forth in the foregoing Example No.1.

Example No. 5

In place of the aqueous solution of magnesium silicofluoride set forthin the foregoing Example No. 1, one may employ a dilute aqueous solutionof hydrochloric acid, according to the same procedure set forth in theforegoing Example No. 1, and for this purpose one has found that a onepercent aqueous solution of hydrochloric acid is satisfactory.

In making the new acoustical tile the best acoustical values andgreatest strength are obtained when the particle size of the vermiculiteis in the intermediate size or range of 16-30-50, as specified in theforegoing Example No. 1.

In making the new acoustical tile in accordance with the formulae setforth above, in Examples Nos. 1 to 5, inclusive, the particle size ofthe vermiculite employed is preferably that which is described below asthe Intermediate Particle Size, although vermiculite having the particlesizes between the maximum and minimum mesh sizes hereinafter referred tomay also be employed, although less advantageously:

MAXIMUM PARTICLE SIZE 7 INTERMEDIATE PARTICLE SIZE Mesh Size 163050Maximum percentage of particles retained on screen 609598 Minimumpercentage of particles retained on screen 206575 MINIMUM PARTICLE SIZEMesh Size 3050100 Maximum percentage of particles retained on screenMinimum percentage of particles retained on screen 15-60-90 Amodification of the invention is illustrated in FIGS. 3 and 4 of thedrawings and embodies the same composition and may be made by either ofthe methods outlined in the foregoing Examples Nos. 1 and 2 except thatin this instance the composition when placed in the mold is spread andcompacted from the center radially outwardly to the walls of the mold soas to provide a relatively dense compacted marginal peripheral edgeportion 15 in the finished acoustical tile. Thus, in this form of theinvention the tile 13 includes a central body portion 14, which is shownas being rectangular in shape, and which has the same density as thebody 11 of the tile 10 shown in FIGS. 1 and 2, but differs therefrom inhaving a relatively dense and compacted marginal peripheral edge portion15 formed by packing the composition around the peripheral edge portionof the mold. This relatively dense marginal or peripheral edge portion15 may be provided with a suitable beveled edge 16.

The provision of the relatively dense marginal edge portion 15,surrounding the center portion 14 of relatively lower density, providesfor better sound-absorption at low as well as high speech frequenciesand provides the tile 13 with a sharp strong marginal edge portion 15which is useful in machining the tile and in fastening it in position ofuse as by nailing or the like. Other forms of variable density in thetile will be set forth hereinafter.

A further modification of the invention is illustrated in FIGS. 5 and 6of the drawings, wherein the tile is generally indicated at 17, andincludes a generally rectangularshaped outer body portion 18 having abeveled edge portion 19. The body port-ion 18 has the same compositionas the body portion 11 in the form of the invention shown in FIGS. 1 and2, or the body portion 14 in the form of the invention shown in FIGS. 3and 4 of the drawings.

However, in the form of the invention shown in FIGS. 5 and 6 of thedrawings one provides the new tile with a generally rectangular-shapedand relatively dense center portion 20 which may have the samerelatively high density as the peripheral edge portion 15 of the tile 13shown in FIGS. 3 and 4 of the drawings, and which enhances the abilityor capacity of the resulting tile 17 to absorb and deaden sounds orsound vibrations in the higher ranges of the sound frequencies inherentin human speech.

A further modification of the invention is illustrated in FIGS. 7, 8 and9 of the drawings, wherein it is generally indicated at 21, andcomprises an acoustical tile body 22 which may embody the composition ofand may be prepared in accordance with any of the foregoing ExamplesNos. 1, 2, 3, 4 and 5, and may be provided with a suitable beveled edge23. However, in this form of the invention one incorporates in the bodyof the tile reinforcing bars 24 and 25, which have base flanges 26 and27, respectively, and are generally V-shaped in cross section and may bemade of a suitable aluminum alloy or other relatively light,corrosion-resistant materials such as thermosetting resins. As shown inFIGS. 7, 8 and 9 of the drawings the reinforcing bars 24 and 25 may bearranged in groups of right-angularly intersecting bars with their baseflanges 25 and 27 arranged in superimposed contacting relationship.

In the use of the form of the invention shown in FIGS. 7, 8 and 9 it hasbeen found that the new acoustical tile units 21 may be made inrelatively large sizes such, for example, as 2 'by 2 square, and whenfastened to or suspended from a ceiling or wall surface have adequatestructural strength such that they will not sag or crack while, at thesame time, possessing the desirable acoustical and fireresistantproperties and other characteristics hereinbefore mentioned.

In the practice of the present invention it has been found that in placeof the vermiculite specified in the foregoing examples one may alsoemploy perlite, which is a naturally occurring form of volcanic rockfrom the western part of the United States and is classified as aperlitic obsidian glassy rhyolite or related silicic glassy volcanicrock varying in texture from porphyritic to glassy gray with pearlyluster and containing a small proportion of water and when crushed (asmined) and carefully heated to a high temperature expands to alightweight cellular material which is from 10 to 20 times its originalvolume and resembles rock wool in texture. (Condensed ChemicalDictionary, fourth edition (1950) Reinhold Publishing Company, page509.) The naturally occurring perlite is mostly found in compacted orunexpanded form but when heated properly to a temperature of about 1600F. it expands significantly and is sold and used industrially in thisform, known as unshattered expanded perlite, which is the form foundmost useful in the practice of the present invention, and which isreferred to hereinafter in the following examples, although one may alsouse the naturally occurring expanded perlite if the same is screened toprovide a product having the desired perlite size herein referred to.

Thus, in the practice of the present invention one may make the newacoustical tile employing expanded perlite, in accordance with theformulae illustrated in the following examples in which all partsindicated are by weight:

Example N0. 6

In making the new acoustical tile employing expanded perlite, in placeof the vermiculite specified in Examples Nos. 1 to 5, inclusive, thesame procedures and conditions set forth in Example No. 1 may beemployed except that in this instance one employs with the asbestosfiber specified in Example No. 1, 8 oz. of screened expanded perlitehaving a particle size of minus 8 plus 30 mesh pnoduced from a rawperlite ore known as PA6 (Schundler) plus 3 oz. of screened expandedperlite known as 0 grade (American Bildrok) and produced from an oreknown as PA100 (Schundler) having a mesh size of approximately 100 andhaving a Weight per cubic foot of from 3 to 5 pounds per cubic foot.

The screened expanded perlite produced from the ore known as PA6(Schundler), referred to above, has the following (American Bildrok)screen analysis:

Mesh Size 8 16 30 50 100 100() Cumulative percentage of particlesretained on screen, by volume Typical screen analysis Trace -95 TraceTrace The screen analysis on the screened expanded perlite known as 0grade (American Bildrok) and produced from an ore known as PA100(Schundler) is as follows:

Mesh Size 16 30 50 100 200 200() Cumulative percentage of particlesretained on screen, by volume Typical screen analysis Trace 97-100 2 9Example N0. 7

In making the new acoustical tile employing expanded perlite one mayemploy with the asbestos fiber in place of the materials specified inthe foregoing Example No. 6, and following the same procedure referredto therein and in Example No. 1, 12 oz. of screened expanded perliteproduced from the raw perlite ore known as PA6 (Schundler) having aparticle size of minus 8 plus 30 mesh and having a weight per cubic footof from 5 to 7 pounds.

Example N0. 8

One may also make the new acoustical tile according to the proceduresset forth in the foregoing Examples Nos. 1 and 6 except that in thisinstance one may employ with the asbestos fiber in place of thematerials specified in Example No. 6, 6 oz. of screened expanded perliteproduced from the raw perlite ore known as PA6 (Schundler) having aparticle size of minus 8 plus 30 mesh and having a weight per cubic footof from 5 to 7 pounds per cubic foot, together with 6 oz. of screenedexpanded perlite known as grade (American Bildrok) having a mesh size ofapproximately 100 and having a weight of from 3 to 5 pounds per cubicfoot.

Example N0. 9

In place of the materials specified in the foregoing Example No. 6, butfollowing the same procedure therein set forth, and in Example No. 1,one may employ with the asbestos fiber, 12 oz. of unscreened expandedperlite produced from raw perlite ore (PA6-Schundler) having an expandedweight of from 6.5 to 8.5 pounds per cubic foot having the followingscreen analysis:

Mesh Size 4 8 16 30 50 50() Cumulative percentage of particles retainedon screen, by volume Typical screen analysis Trace Example N0. 10

In place of the materials specified in the foregoing Example No. 6, butusing the same procedures therein specified and in Example No. 1, onemay employ with the asbestos fiber, 12 oz. of unscreened expandedperlite produced from raw perlite ore known as PA3 (Schundler) having aweight of from 5 to 7 pounds per cubic foot and having the followingscreen analysis:

Mesh Size 8 I 16 l 30 50 I 100 I100(-) Cumulative percentage ot'particles retained on screen,

by volume 0-2 -25 35-65 65-90 90-100 0-10 Typicalscreen analysis. Trace22 58 80 95 5 In the practice of the present invention one may alsoemploy mixtures of vermiculite and expanded perlite. Thus, the newacoustical tile may be made in accordance with the following examples inwhich all parts indicated are by weight:

Example N0. 11

10 Example N0. 12

In making the new acoustical tile in accordance wit-h the presentinvention one may also employ the procedures set forth in Example No. 1but employing a mixture of 6 oz. of vermiculite having a mesh size of30-50-100 and 6 oz. of expanded screened perlite having a mesh size ofminus 8-plus 30, as above described.

Example N0. 13

One may also make the new acoustical tile following the procedures setforth in the foregoing Example No. 1 but employing a mixture of 3 oz. ofvermiculite having a mesh size of 16-30-50 and 9 oz. of expandedscreened perlite having a mesh size of minus 8-plus 30, as abovedescribed.

Example N0. 14

One may likewise employ a mixture of 3 oz. of vermiculite having a meshsize of 16-30-50 and 9 oz. of expanded perlite having a mesh size ofminus 8-plus 30, as above described.

In making the new acoustical tile employing a mixture of vermiculite andexpanded screened perlite, as in the foregoing Examples Nos. 11, 12 and13, the particle sizes of the vermiculite and of the expanded screenedperlite are preferably in the intermediate range, as set forth above, inorder to afford the best acoustical values and the greatest strength inthe new acoustical tile.

As hereinbefore indicated, one may employ naturally occurring expandedperlite in any and all of the foregoing Examples Nos. 6 to 14,inclusive, and in the same amounts, or mixtures of the two forms ofperlite referred to above, provided the material has been screened tothe proper particle sizes above set forth.

It has been determined, by standard reverberation room tests made by arecognized acoustical laboratory, that the Noise Reduction Coefiicient(N.R.C.) of an acoustical tile made in accordance with the foregoingExample No. 1, employing vermiculite, was 0.75 for a No. 7 mounting and0.65 for a No. 2 mounting. The definitions of these terms are thosegiven in Bulletin No. XVI of the Acoustical Materials Association, pages5 and 6. The tile tested were 12" x 12" x A in size and had a density of1.6 pounds per square foot, unpainted. The area tested was 72 squarefeet.

In another test by the same acoustical laboratory, made with an acoustictube in accordance with the A.S.T.M. Standard Method of Test forImpedance and Absorption of Acoustical Materials by the Tube Method, ona specimen of the new acoustical tile made in accordance with theforegoing Example No. 6, and employing expanded perlite, rather thanvermiculite, the statistically computed N.R.C. was 0.60. The test wasmade on an unpainted specimen of tile 12" x 12" x A" With a Ms air spacebehind the specimen.

In the case of acoustical tile made in accordance with the foregoingExamples Nos. 7 and 8, and employing a mixture of vermiculite andexpanded perlite, an acoustic tube test by the same laboratory on twospecimens of the new acoustical tile gave an N.R.C. of 0.635. Thespecimens were 12" x 12" x 78'', unpainted, and the air space behind thetile was one inch.

It has been found that an improved and even more highly dimensionallystable, water-resistant and moistureresistant acoustical tile may bemade by the addition of urea to the sodium silicate binder employed inthe foregoing examples. This aspect is disclosed in detail in theapplication Serial No. 677,194, but the following examples will sufliceto explain fully the use of a binder employing an aqueous dispersion ofsodium silicate modified by the presence of urea. Moreover, the exampleimmediately following will describe what has been found to be a highlyadvantageous drying procedure for drying the corresponding molded tileproduct.

1 1 Example N0. 15

The general procedure outlined in Example No. 1 is followed up to thepoint where the final binder is to be employed, and instead of thebinder of Example No. 1, a binder is prepared in the form of an aqueoussolution or mixture of sodium silicate and urea which is then thoroughlymixed wit-h the composite bodies prepared as above. For this purpose itwas found that for the quantities of vermiculite and asbestos indicatedabove in Ex ample No. 1, from 20 to 28 02., with an optimum of 26 oz.,of an aqueous solution of sodium silicate, known as the so-called No. 40(Diamond Alkali Company) sodium silicate, mixed with one (1) ounce of awater solution of urea, which will be described hereinafter, is verysatisfactory, the sodium silicate solution, before addition of the ureasolution, having a specific gravity of 1.381.40 (40.00-41.50 B.) with anaverage solids content of 37.5 percent. The urea solution is prepared bythoroughly mixing one to two ounces of urea prells (Grace ChemicalCompany, Technical Grade) in one pint of Water (preferably distilled).The operation of mixing the treated vermiculite and asbestos with thesodium silicate-urea binder is continued for a period of from one to twominutes, whereupon the composition assumes a golden brown color.

A heat-resistant metal screen is set in complementary recesses in a gridin the bottom of a mold which is then filled with the:as-bestos-vermicu1ite-binder composition, prepared in accordance withthis example. The composition is then compressed to a thickness ofwhereupon the resultant tile and screen are removed from the mold byknock-out pins and placed in an infra-red drying oven, at 500 watts, foran initial heating period of twelve (12) minutes at a temperature whichdoes not exceed, at this stage 210 F. in the tile body. The heat is thenoff for a period of six (6) minutes, whereupon the heat is thenreapplied at 500 watts, for a further period of six (6) minutes. Theheating operation is then discontinued for a period of six (6) minutesand the on-otf heating cycle then continued for a total on-off heatingtime of sixty (60) minutes, including the initial six 6) minutes. Duringthe final stages of the heating operation the temperature in the tilebody may reach 320 F. or higher. This results in complete cure of thetile. After drying, the tile and screen are separated. This procedure,further details of which are set forth below, has been found to behighly effective in preventing warping of the tile, which is otherwisehighly susceptible to distortion during drying, and in producing auniformly fiat acoustical tile.

After the resulting tile form or shape has been thus. dried, but isstill hot, it was found, that to further enhance the desired stabilityand resistance to moisture absorption in the binder, and freedom fromw-arpage and buckling in the new tile, it should be treated as in Exam-.ple No. 1 with an aqueous solution of magnesium silicofluor-ide(Magnesium flu-osil-icate) (from 3 to 20 percent), which may be appliedas by spraying the dried tile, or preferably added to urea as will beexplained, so as to thoroughly impregnate the entire mass including theso dium silicate-urea binder.

The procedures set forth in Example No. 15 can be likewise substitutedin other of the examples following Example No. 1. The amount of the ureasolution used with the sodium silicate solution can be varied, and theconcentration of the urea solution can be varied by em ploying more orless of the urea prells. Moreover, an aqueous solution of ammoniumsili-co-liuoride (ammonium fiuosilicate) or hydrochloric acid can besubstituted for magnesium silico-liuoride, thusly;

Example N0. 16

In place of the aqueous solution of magnesium silico fluoride, MgSiF .6HO, referred to in Example No. 15, an aqueous solution of ammoniumsilicofluoride (ammonium fiuosilicate) (NH )2SlF can be used. F or thispurpose one may employ a one percent aqueous solution of the saidammonium silieofiuoride according to the same procedure set forth in theforegoing Example No. 15.

Example N0. 17

In place of the aqueous solution of magnesium silicofluoride set forthin Example No. 15, one may employ a dilute aqueous solution ofhydrochloric acid, accord-ing to the same procedure set forth in ExampleNo. 15 For this purpose it has been found that a one percent aqueoussolution of hydrochloric acid is satisfactory.

In this instance, moreover, one may employ fourteen (14) oz. ofso-called grade No. 3 vermiculite and two (2) oz. of so-called grade No.7D04 asbestos in preparing an acoustical tile having the dimensionsspecified in Example No. 15.

Example No. 18

In place of the materials specified in the foregoing Example No. 6, butfollowing the same procedure therein set fotrh, and in Example N0. 1,one may employ with defiberized asbestos fiber six (6) oz. of perli'teknown as concrete aggregate weighing approximately eight and one-half (8/2) pounds per cubic foot and produced from per-lite ore found inFlorence, Colorado, (Great Lakes Carbon Corporation) and five (5) oz. ofplaster grade aggregate weigh-ing seven and one-fourth (7%) pounds .percubic foot produced from the same ore.

The concrete aggregate weighing eight and one-half (8 /2) pounds percubic foot has the following screen analysis:

The plaster grade aggregate weighing seven and onefourth (7%) pounds percubic foot has the following screen analysis:

Mesh Size I 16 l 30 50 I 100 Pan Cumulative percentage of particlesretained on screen, by volume 57 Example N0. 19

In making the new acoustical tile, employing a mixture of expandedperlite, one may follow the procedure set forth in the foregoing ExampleNo. 15, as in Example No. 18, but employing a mixture of nine (9) oz. ofconcrete aggregate weighing eight and one-half (8 /2) pounds per cubicfoot with a particle size as set forth in Example No. 18, and three (3)oz. of plaster grade aggregate weighing seven and one-fourth (7%) poundsper cubic foot, and having a mesh size as set forth in Example No. 18above.

In the above case of acoustical tile made in accordance with theforegoing Examples Nos. 15 and 18, an acoustic tube test by theabove-identified laboratory on two specimens of the correspondingacoustical tile gave a noise reduction coefiicient at 250 cycles of 0.27and 0.76 at 500 cycles with the material abutted tightly against a steelplate, and with no intervening air space.

In the case of the acoustical tile made in accordance with the foregoingExamples Nos. 15 and 19, an acoustic tube test by the same laboratory ontwo specimens of the corresponding acoustical tile gave a noisereduction coefiicient of 0.28 at 250 cycles and of 0.66 at 500 cycles,also with the material labutted directly against a steel plate and withno interveningspace.

It has been further found that the acoustical properties and overallstructural characteristics of the tile can be enhanced by following thegentle mixing procedure outlined in Example 20 to immediately follow.Example 20 will include incidental reference to the nature of purchaseditems and equipment used in order that there can be an exactingappreciation of the entailed method and mixing procedure.

Example No 20 The original mixture is composed of Schundler PA4' perliteexpanded to produce a weight of 6 to 6 /2 lbs. per cubic foot, andasbestos fiber designated by Johns Manville as 7DO4. This mixture ofperlite and asbestos may be varied with the view of changing the overallsound control characteristics of the final product. Thus, the variationmay be such as 12 ounces of perlite and 2 ounces of asbestos fiber, orthe variation may be of a perlite having a variance of screen analysisand in this case either more or less perlite may be used or more or lessasbestos fiber may be used, but the foregoing procedure represents anacceptable standard.

The asbestos fiber is received from the producing mill either in burlapbags or compacted in paper bags weighing 100 lbs. The fiber, whenreceived, is in partially compacted state, and as a result when droppedfrom the container on the floor and in this manner broken up, there willbe many small balls of fiber ranging in diameter of from a quarter of aninch up to as much as one inch. It is necessary that this fiber beintroduced into the dry mixing process in the present instance in acompletely finely divided form. Therefore, the fiber is placed in a gyroscreen having a mesh opening of of an inch. The violent action of thisgyro screen causes the fiber to separate which is dropped into a bin inthis separated form. It is important that this asbestos fiber not bepicked up by hand nor stepped on nor in any way compressed, because itwould then go back into a mass that would not permit a properdistribution of the individual fibers in the dry mixing apparatus.

Thus, the now finely divided asbestos fiber particles are picked up in ametal scoop, weighed and transferred to the dry mixer that has alreadybeen charged with 33 lbs. of dried perlite. The asbestos fiber, i.e., 9lbs. of asbestos fiber thus resulting in a total charge of 42 lbs., isplaced on top of the perlite in its finely divided form. Since theasbestos is heavier than the perlite particles, it is introduced on topof the perlite in the mixer so that during the mixing process it willgradually work its way through the entire mass, and individual particlesof asbestos become attached to the perlite glass envelope particleseither through a mechanical attachment or through a phenomenon ofelectro-attraction, as explained above and depicted in FIG. 10.

Mixing is gently conducted continuously for a period of two minutes inwhich time the finely divided particles are completely and properlydispersed and in part temporarily joined together as aggregateasbestos-perlite bodies. If the asbestos fibers were introduced as notproperly separated by the gyro screen, then in the finished productsmall lumps would appear on the surface thus detracting from a desirableappearance and acoustical value.

The two minute mixing process is more or less critical, because werethere to be over-mixing the small perlite glass envelopes would likelybe unduly fractured thus destroying the desired acoustic nature of theperlite in spite of the asbestos protection suflicient during thecritical period. Therefore, great care must be used so as to not exceedthe critical mixing period. This is easily accomplished by controllingthe mixer with a time switch which automatically stops the mixing atthis point. Details of entailed equipment are shown commencing with FIG.11 and will be explained under the separate heading PLANT OPERATIONbelow.

This asbestos-perlite aggregate body mix is now to be thoroughlywater-proofed and in part the asbestos fibers permanently bound to theperlite glass envelopes, so that when the final binder is subsequentlymixed in, the final binder will not penetrate the asbestos fibers ormineral particles, but will form a matrix to contain them, and so thatthere will be no further fracturing of the perlite envelopes.

This is accomplished by now introducing one pint of a water-proofingbinder solution composed of one-half pint of Dow-Corning XS-l and/orXS-Z silicone resin mixed with one quart of water. In order toaccomplish this, the mixer is equipped with a one quart tank which inturn is connected with a large mixing tank where this solution, throughthe use of an air motor attached to a shaft with four-bucketedpropellers properly arranged thereon, is kept in constant agitation andalso under pressure. The operator at the mixing machine turns the valveand fills the container attached to the mixer with one pint of thissolution. He then opens another valve, and the solution runs by gravityinto a mixing valve where air is introduced, and the solution then inthe form of a finely divided spray is sprayed into the mixer in motioncontaining the aggregate bodies. It requires 35 seconds to properlyintroduce this pint of material in its finely divided form resulting inthe covering of every fiber and particle in the mixture, thus providinga bond between the asbestos fibers and the perlite and the entiremixture becoming highly non-hygroscopic.

The material is now wet to the extent that the major portion of the pintof aqueous solution has been introduced. Therefore, in order to set thesilicone binder and develop a permanent bond, it must be thoroughlydried. In order to accomplish this drying, two infra-red gold reflector4-rod quartz lamps backed up with gold reflectors are attached to themixer. These lamps are controlled by the time switches. Each quartz lampis composed of a rod 16 inches long having a capacity of watts per inch.Thus eight of these quartz lamps when activated would produce a littleover twelve kilowatts.

Were this mixture to be put into continuous motion during the dryingprocess, here again the perlite glass envelopes would tend to be brokenup and the acoustics in the end product destroyed. In order to guardagainst this, the time switch means for controlling the mixer isselected to operate as follows: for ten minutes the quartz lamps are on,at the end of each minute, the mixture is activated for only one secondand then stopped, gently turning over the mass in the mixer andpermitting it to be exposed to the infra-red lamps. This operationcontinues for a period of ten minutes, and the mass in the mixer hasbeen in action during this time for a period of only ten seconds, i.e.one second at the end of each minute.

The mass of aggregate asbestos-perlite bodies has now been treated withthe organic silicone and dried and is now ready to be discharged fromthe mixer. Thus, this mixer is located above the mixer where the finalbinder solution of sodium silicate and urea is introduced. Transfer anddischarge takes place through a gate automatically operated with an aircylinder and air valve and the transfer is to the wet mixer. Thedischarge period is approximately twenty seconds.

The permanently bonded bodies are now in the wet mixer. This mixer,insofar as the mixing action is concerned, is designed exactly as thedry mixer described above. However, this mixer is equipped with afifteen gallon tank having a 2 /2 inch valve with a 2 /2 inch pipe twofeet long attached to the bottom thereof and leading down into the wetmixer through a cover. This pipe is swaged so as to have a flanged endopening of approximately of an inch. It should be mentioned that both ofthe mixers have hinged covers. During the drying process in the drymixer, its cover remains open so that any moisture or steam may escapeduring the drying operation.

The tank associated with the wet mixer is equipped with mixing paddles.It will be recalled that the dry mixer was charged with a combination ofasbestos and perlite having a total weight of approximately 42 lbs.Accordingly, the tank associated with the wet mixer is to be filled withapproximately 72 lbs. of 40 to 41 Baum sodium silicate.

Were the sodium silicate to be introduced as plain sodium silicate, theresulting product when dried out would be highly hygroscopic and not ascapable of retaining its original dimensions. If submerged in water, itwill break up. Hence, if placed on a ceiling and the relative humidityin the room was normal or above normal it would probably undergodimensional change; were the four corners securely attache-d, it woulddroop into a cup formation. Obviously, under these conditions commercialvalues are not as good as otherwise.

Therefore, in order to eliminate this condition, the following ureasolution is added to the sodium silicate aqueous solution, namely, twoounces of urea, preferably as an equal mixture of urea prells and ureapowders, to one pint of water. It is important that this urea solutionbe prepared in a fifty gallon tank and kept constantly under agitationwith an air motor having attached thereto bucket propellers operating ata slow speed. Otherwise, the urea will separate out of solution veryrapidly unless agitation is constant. The amount of this solutionintroduced into the sodium silicate is highly critical. Were there to betoo much, there would be an eventual excessive gas (probably ammonia)evolution causing distortions or eruptions in the tile product in theform of lumps over the surface of the dry tile, thus detracting fromappearance and resulting in an indeterminate density in the end acousticproduct. Likewise, if the urea solution is not properly dispersedthrough the sodium silicate, this same situation where the urea solutionwas concentrated would again through the action of evolved gasses causebumps or bubbles to occur over the surface of the resulting dryacoustical tile. Therefore, when the urea solution as above describedhas been introduced into the sodium silicate, the sodium silicate andthe urea solution must be subjected to violent agitation in the mixingtank by rapidly turning in one direction and then the other the mixingpaddles or propellers.

Because of the critical characteristics of this operation, it is highlyadvantageous that the urea solution and the sodium silicate solution bemixed in reasonably small batches so that absolute control both asapplied to quantity and mixing action may be obtained.

With the urea and sodium silicate now combined and with the dry materialnow reposing in the wet mixing unit, the-2V2 inch valve, which is a slipvalve, is opened simultaneously with the activation of the mixer anddischarge of the binder solution into the wet mixer is commenced. Thedischarge time is approximately twenty-five seconds. The total mixingtime, including the discharge time, is one minute thirty seconds to oneminute and forty-five seconds, accurately controlled again through theuse of time switches. It is important to avoid excessive mixing toassure as little breakage as possible of the fragile perlite envelopes.

The primary advantage of the perlite or vermiculite particles is thatthese materials, especially in expanded form, represent minute hollowparticles presenting communicating air spaces which contribute to orresult in good acoustical, that is, sound absorbing properties. Theacoustical properties are further enhanced by using one or both of thesematerials in combination with asbestos, and in this connection it willbe recalled that by first coating the mixed materials including asbestoswith a silicone resin or like compatible water-repellent binder adhesivethe asbestos fibers build up arou d the perlite or vermiculite particlesand protect these against crushing during subsequent mixing and molding.This condition is illustrated in FIG. 10 of the drawings. In thisfigure, the reference character P indicates the perlite or vermiculiteparticles, and the reference character A identified the asbestos fibers.Thus the asbestos fibers are occluded in a pile array about the tendervermiculite or perlite particles P, and this becomes a permanent unionin the presence of the dried silicone resin hinder or likewater-repellent coating material. The presence of the pile arrayrepresented by the asbestos fibers A thus presents in effect an outershield that protects as many of the particles P as happen to be presentin a bundle or agglomerate body, and hence the likelihood of crushing orfracturing the particles P is greatly reduced so that in the finalpro-duct the original form of the particles P is for the most partmaintained, and additionally the pile array preserves some spacingbetween adjacent agglomerate bodies, such agglomerate body beingindicated as a totality by the reference character AG in FIG. 10.

It has been further found, however, that acoustical tile acceptable forinstallations where the sound to be absorbed is not so severe, can beprovided by omitting the asbestos so long as the perlite or vermiculiteparticles are first mixed in the presence of a silicone resin or likesubstantially water-repellent fire-resistant binder adhesive. Thus, itso happens that by following such procedure wherein the asbestos fibersare omitted, the perlite or vermiculite particles collect together andball-up into small aggregate bodies containing many of the individualperlite or vermiculite particles bonded together into the lumpaggregates by the silicone resin or like binder adhesive which becomesan internal binder. Hence, when these aggregate bodies are further mixedin the presence of the fire-resistant final or external binder asrepresented by sodium silicate or the like, which is preferably highlywater-repellent, those particles within the center of the aggregatebodies are protected against crushing or break-up by the outer-most skinor shell of perlite or vermiculite particles. The nature of theaggregate bodies not including asbestos fibers is illustrated in FIG.10A. In this instance, the aggregate bodies AG comprise individualparticles P of perlite or vermiculite bonded together by the siliconeresin binder SB. This is the state of the material as it is passed intothe wet mixer where the sodium silicate binder is to be applied. Thissame protection is afforded during the final molding under pressure. Thefollowing is an example of acoustical tile produced by omitting asbestosin accordance with the foregoing:

Example N0. 21

The general procedure set forth in connection with Example No. 20 isfollowed, except that for each 12 x 12 x tile there is used twelveounces of Schundler PA4 expanded perlite weighing 6 to 6 /2 pounds percubic foot, and no asbestos is mixed therewith. Rather, the initiallydry mass charged into the mixer consists only of the re quired amount ofsuch perlite predetermined as a proper batch for producing apredetermined number of acoustical tiles, and after the mixer has beenso charged the waterrepellent binder material consisting of a waterdispersion of the silicone resin set forth under Example 20 isintroduced gradually into the mixer and the mass agitated lightly todisperse the binder uniformly among the perlite partciles. This causesthe perlite particles to collect together into aggregate bodies untilthe resin is completely absorbed. The binder is then set up andthoroughly dried under infra-red heat in the manner explained inconnection with Example 20 under circumstances of gentle turn-over ofthe aggregate bodies containing the binder to further assure as littlefracture as possible of the perlite particles.

The mass is then transferred to the wet mixer where the final sodiumsilicate water solution containing urea is introduced in accordance withthe procedure of Example 20, and it was explained that the urea for somereason or other greatly enhances the dimensional stability of the finalproduct by somehow rendering the sodium silicate more resistant tomoisture absorption. It has also been found that tile can be produced inaccordance with the present invention having even higher resistance towater or moisture absorption by mixing a silico-fiuoride directly withthe urea fortified sodium silicate solution. The following are examples:

Example No. 22

The same procedure as in Example 21 is followed except that the final orexternal binder is one composed in the following manner and proportions:a solution of two ounces of urea prells and one-quarter ounce ofmagnesium silico-fluoride in one pint of water, and three-fourths ouncesof this solution is added to twenty ounces of 41 Baum sodium silicate.This solution, by increasing the amount of sodium silicate can also beused for tiles that are to include asbestos, as set forth in thefollowing example:

Example N0. 23

The general procedure of Example 21 is followed except that elevenounces of the perlite are mixed with two to three ounces of asbestosfibers before the silicone resin internal binder is added. Use of thisbinder also results in aggregate bodies of perlite particles asexplained above in connection with Example 21, and these bodies arefurther protected against crushing of the perlite particles due to thetendency of the asbestos fibers to occlude to the outer surfaces of theaggregate perlite bodies providing a protective outer pile, and thiscondition is permanently maintained by the silicone adhesive dried underheat. In affording the final sodium silicate binder, there is used thesame general binder set forth above in the immediately preceding exampleexcept that two ounces of urea and-one-quarter ounce of magnesiumsilico-fiuoride were mixed in one pint of water and one ounce of thissolution was added to 26 to 28 ounces of 41 Baum sodium silicate.

It is believed that the advantageous effect of urea on the sodiumsilicate is one deriving from its pH characteristics in disassociation,that is, urea when heated disassociates releasing ammonia which producesa chemically basic condition within the body of the moist tileundergoing drying, thereby contributing to the achievement of a highlyeffective binding action of the binder derived from sodium silicate. Thefinal binder very probably is a complex of silica. It has been foundthat there are substitutes for urea, but with possibly one exception,namely, diethanolamine, these are not as efiicacious as urea. Moreover,urea is a relatively inexpensive material and one that is readilyavailable on the market. Thus, it has been found that a solution of ureacan be substituted by solutions of other basic ingredients includinginorganic such as magnesia (MgO), calcium hydroxide and sodiummonohydrogen sulfate (Na HPO .10H and organic bases including pyridine,triethanolamine, ethanolamine and diethanolamine. These substitutesprobably produce a strong basic condition within the tile immediatelyupon addition, in contrast to urea. All of these materials are lessbasic than sodium silicate, having a pH value of about 7 or better. Intesting these materials capable of substitution for urea, one ouncethereof was dissolved in one pint of water just as one ounce of urea wasdissolved in one pint of water as the preferred urea concentration inthe corresponding examples described above.

The resultant solutions were individually used in substitution of theurea solution in corresponding individual test tiles composedessentially of perlite mineral particles that were first coated with asilicone resin binder followed by sodium silicate modified by theparticular urea substitute. After the test tile bodies had been made up,each was submerged in water at room temperature and loaded 18- at thecenter with a five-ounce dead weight. The time at which each tile brokeunder the weight was noted, and the following data tabulated:

PLANT OPERATION FIGS. 11 to 20 inclusive are devoted to a showing ofessential production equipment used to manufacture acoustical tile inaccordance with the present invention, as Well as certain details of thefinished product. These figures are not drawn to scale and are more orless schematic in most respects. Referring to FIG. 11, the needed weightratios of the dry ingredients which will consist of the perlite orvermiculite particles and the asbestos fibers, if the latter are to beused, are charged as gently as possible into a mixer which is equippedwith mixer blades (not shown) that are rotated by a propeller shaft 111which in turn can be considered as driven by a belt and pulleyconnection driven by a drive motor DM. Where asbestos fibers are to beused, these, being heavier than perlite or vermiculite, are added to thedry mixer after perlite or vermiculite. Being heavier, the asbestos willgradually work its way down through the perlite or vermiculite duringpreliminary mixing which occurs uninterruptedly for only two minutes inorder that the perlite or vermiculite envelope-type particles will notbe unduly broken or crushed one on another.

It will be recalled that the dry ingredients charged into the dry mixer100 are to be lightly or tenderly agitated in the presence of afire-resistant water-repellent adhesive or binder represented by asilicone resin or the like as explained above, and which occurs as acoating entirely about the particles assuring complete water repellency.This binder adhesive can be advantageously supplied from a container 112mounted adjacent the dry mixer 100, suitable spouting and valving meansbeing afforded to enable the binder resin to be sprayed in mist forminto the mixer 100 in the desired amount and at the desired rate whichconsumes less than one minute. In order that gentle mixing and turn-overof the ingredients can be accomplished in the dry mixer 100, this mixeris equipped with a control box CB which includes a known kind ofselectively settable timing means for periodically energizing the drivemotor DM. It should be pointed out that the top of the dry mixer 100 isequipped with a lid (not shown) and the lid is equipped with heaterelements 115 which comprise infra-red quartz lamps, and associatedreflectors, which are energized after the resin binder has beenuniformly dispersed among the dry ingredients charged into the dry mixer100, and upon energization the heater elements remove water and causethe binder resin to set up and harden producing a permanent innercoating about the perlite or vermiculite particles. These lamps areturned on for ten minutes, assuming a dry charge of 33 pounds of perliteand 9 pounds of asbestos, and a charge of one pint of water-dispersedsilicone resins. During the time the lamps are on, the agitator in thedry mixer is automatically operated for but one second only every oneminute. In the presence of asbestos, the asbestos fibers are at the sametime permanently afiixed by the silicone binder to the mineral particlesin a protective pile array; or in the absence of asbestos fibers, themineral particles represented by perlite or vermiculite are themselvesagglomerated into larger size particles wherein the innermost particlesin each agglomerate bundle of particles are protected by the shell ofoutermost particles, and this of course occurs to a certain extent evenwhere the asbestos fibers are present.

After the foregoing has been accomplished, a gate in the mixer 100 isopened and the bonded dry bodies are discharged through a funnel 120into the so-called Wet mixer 121, and it is here that the final binder,in the form of sodium silicate or like siliceous water-solublefire-resistant binder adhesive is added. The structural details of thewet mixer are similar to those of the dry mixer in that the mass in thewet mixer is to be turned over by agitating blades that are operatedperiodically in a brief, gentle manner by a drive motor DMZ controlledby timing elements in a control panel CB2.

The sodium silicate or like binder is admitted from a tank 123 that ismounted on the wet mixer, and materials such as urea, magnesiumsilico-fiuoride and the like, which are used to modify and enhance theeffect of the sodium silicate, are mixed with the latter in the tank 123for simultaneous admission with the sodium silicate into the wet mixer.For the charge mentioned above, approximately 72 pounds of 4041 Baumsodium silicate is used, and this advantageously modified with urea, andmagnesium silico-fluoride. The wet mixer 121 is not inasmuch as thesilicate binder is dried out and permanently set up in heat chambers tobe described hereinafter.

The time required to introduce the material from the tank 123 is about25 seconds, and the total mixing time in the Wet mixer inclusive of thisis about one and onehalf minutes for the above-identified charge as setby timing switches again to assure no more mixing than the minimumnecessary.

Once the materials in the wet mixer have been mixed to the desiredextent, the discharge gate of the wet mixer is opened and the moist massfrom which the acoustic tile are to be made is discharged through afunnel onto the lower end of an inclined conveyor belt 125 which carriesthe moist mass to a filling station where individual acoustical tilemolds are to be filled therewith as will be explained.

The plant installation in the present instance is preferably set up sothat advantage is taken of gravity flow for charging and discharging themixers 100 and 121. Such installation eliminates the need forintermediate feed conveyors into and out of the mixers, and conserves agreat deal on the square footage of the plant structure. In other words,the dry mixer 109 is located at an elevated position immediately abovethe wet mixer 121, and the wet mixer 121 in turn is located at anelevated position slightly above the lower end of the conveyor belt 126.Thus as shown in FIG. 11, the conveyor belt 126 moves in an upwarddirection proceeding forwardly from the wet mixer 121, and the endlessconveyor 126 reverses at a point elevated somewhat above a table 130which represents the location of the filling station. This table 130 islocated approximately at what is considered normal table height for anindividual, since individual workers are employed for filling theacoustical tile molds.

The tile molds consist essentially of two main parts, namely, a moldtray 132, FIGS. 12, 13 and 14 and a stripper pallet in the form of ascreen or perforate plate 133, FIGS. 12 and 15. The stripper screenserves three main purposes. First of all, it enables the tile, after thesame have been densified in a manner to be explained, to be easilyremoved from the mold trays 132, and at the same time thereby supportedduring the drying operation. Secondly, the stripper screens areconfigured in such a manner as to cooperate with a complementalconfiguration at the bottom of the mold trays which accounts for ahighly advantageous density variation in the tile. Third, the stripperscreen 133 enables the tile product when supported thereby in an oven tobe uniformly heated and baked.

The mold tray 132 is of course of rectangular dimension and has fourvertical side Walls 1325, FIG. 12, which have a vertical dimension (1%)predetermined as adequate to define a mold cavity into which will bedeposited a quantity of the moist mix relayed to the filling station bythe conveyor belt 126. Of course the top of each mold tray 132 is opento enable the filling operation to be performed, and the bottom of themold cavity afforded by the mold tray 132 is defined by a plurality ofspaced bars 136 and 137, the spaces between the bars being exposed atthe bottom of the mold tray, which is to say that in appearance thebottom of the mold tray as shown in FIGS. 12 and 13 is in the nature ofa grid. The bars 136 and 137 are rigidly joined to two opposed sidewalls of the mold tray by necked-down ties 136T and 137T, respectively,and are joined to one another at the midpoint of the tray bottom by likenecked-down intermediate ties T. As shown in FIG. 12, the ties T and theties 136T and 137T are rectangular in cross section as are the bars 136and 137, and the fiat top surfaces of the ties are located below the topsurfaces of the bars so that there are in effect three cross channels atthe bottom of the mold tray. The ends of the bars 136 and 137 adjacentthe side walls of th tray 132 are depressed at 138 and 139, FIGS. 12, 13and 14, just prior to merging into the ties 136T and 137T.

Each stripper screen 133, FIG. 15, is so shaped as to have a pair ofside cross bars 140 and 141 along two side margins which will fit intothe corresponding two channels defined by the necked-down ties 136T and137T leaving exposed the depressions 138 and 139 as shown in FIG. 12.The screen 133 has an intermediate cross bar 142 which will fit in thechannel defined by the aligned and. similarly dimensioned ties T in themold pan. The screen 133 also includes spaced transverse bars 145 and146 which will fit in the spaces between the bars 136 and 137, and thescreen also includes a pair of end bars 148 and 149 which are joined attheir ends to the ends of the side bars 146 and 141 to complete a closedbar rectangle defining the periphery of each screen 133. All of the barscomprising the screen are of the same cross-section dimension. It shouldfinally be pointed out that each screen 133 is thin in comparison to thebars 136 and 137 of the mold tray. Consequently, when a screen isproperly fitted in a mold tray or pan 132, the top surfaces of the bars136 and 137 project above all of the bars of the screen 133 as will beevident in FIG. 12 wherein there is shown at what constitutes a moldloading station a tray and screen assembly ready to move to the fillingstation. A screen when mounted in its mold tray completely closes allspaces at the bottom of the tray, but the tray bars 136 and 137,projecting above the screen bars, account for a variable density in anda rib effect at the back of the title as will be explained.

It was mentioned that the filling station is generally defined as tolocation by a table 130 and that the moist mix carried by the conveyorbelt 126 is dropped in piles on to the table 130. Such occurs at theleft hand side of the table 130 as viewed in FIG. 11. A mold and screenassembly is illustrated in FIG. 11 as located accurately in alignmentwith a rectangular opening in the table 130. The tray or pans 132 arecarried by an endless conveyor 1511 represented by pairs of endlesschains driven by sprockets 151, FIG. 11, and 152, FIG. 16. There arethus two runs or passes of the conveyor 150, namely, an upper pass tothe right as viewed in FIG. 11 which moves the assembled pans andscreens along the production line, and a lower pass to the left whereempty mold pans 132 are inverted. As the empty pans 132 travel to theleft, FIG. 11, the sprockets 151 reverse their direction of travel, anda pan at the sprockets 151 is gradually moved from an inverted orupside-down position into an upright position adjacent a roller conveyor155 where clean screens are available as shown in FIG. 12. This is themold loading station. There is a worker here who removes a clean screenfrom the conveyor 155 and deposits this screen properly in the bottom ofthe mold tray 132. This tray and screen assembly is moved by theconveyor 150 to the filling station beneath the table top 130.

When this assembly is properly registered with the filling opening inthe table 130, approximately half the amount of the moist mix to beeventually pressed is deposited in the open mold cavity. This ratherloose and uncompacted quantity mix fills the mold cavity, whereupon acompacter head 156 is pulled down manually by handles 157 to compressthe mass that was scraped into the open mold cavity. The compacter head156 is of rectangular shape to move neatly into the mold cavity, and asshown in FIG. 11 the compacter head has bars 156B arranged in grid formcomplemental to the construction of the assembled mold at the fillingstation. Hence, the moist mass has a differential density due to thecooperating bars 156 and 136-7, FIG. 11A. Downward movement of thecompacter head occurs against the resistance of a coil spring 160. Thus,the compacter head 156 is supported by a shaft 161 which is guided by afixed sleeve 162, the latter being supported in a fixed position bysupport arms 164. The shaft 161 is provided at its upper end with across head 165 fixed {thereto, and it is the cross head 165 whichcompresses the spring 160 as an incident to a downward pull on thecompacter head 156. When the compacter head is released after lightlycompacting the material in the mold, the spring 160 accounts for areturn movement of the compacter head to its normal elevated or releasedposition illustrated in FIG. 11.

After the wet mass first added to the mold cavity has been partiallydensified by the compacter head 156 to the state X, FIG. 11A, theremaining amount of the moist mass Y, FIG. 11A, which is to compose theparticular tile is then deposited in the mold cavity to fill the same,the top of the mass is leveled off level with the table top 130 and theconveyor 150 is activated to move the filled tray toward the finalpressing station where a ram, as will now be explained, is effective topress the material in the mold to its final thickness dimension.

It should here be pointed out that foot-operated control means (notshown) are provided for separately operating a pair of stops 158 and 159which can be considered as pivoted respectively at 158P and 1591 inposition to stop one filled tray 132A beneath the ram and another filledtray 132B at a point intermediate the ram and the filling station. Thetrays are fixed to the conveyor 150 in a spaced relation that isdetermined by the spacing between the several stations along the lengthof the conveyor chain 150, and hence when a stop is down the conveyor150 is stopped. In this connection it should be mentioned the sprockets151 and 152 are driven by a motor (not shown) that includes a slipclutchcoupling to the drive shaft for the sprockets 151 and 152.

The stops 158 and 159 can be considered as under control of operatinglinks 158L and 159L, FIG. 11, and these links in turn are part of theaforesaid control that preferably is supervised manually by the workersat the filling station and the ram station. Thus, stop 159 should not bereleased until after the ram is effective in a manner to be explained,and stop 158 should not be released until after a mold has been filledand finally leveled at the filling station. Release of both stops isrequired to enable the conveyor 150 with its trays to move on.

Moreover, means are associated with the table 130 to raise and lower thetable, and while such means can take many different forms this can beconsidered as accomplished by toggle link structure L, FIG. 11, whichresponds to the action of the stop block control link 158L. In otherwords, the connections including the links L are selected as a knownmechanical linkage which need not here be illustrated and which willcause the table top 138 to be lowered to the top plane of a mold tray152 at the filling station, so that the material in the mold can beaccurately and easily leveled off at the time when the stop 158 is downin blocking position, and which will allow the table top to be raisedenabling the filled mold to easily pass therebelow and a new mold tomove into filling position when the stop 158 is up in a releasedposition.

Thus, as will be observed in FIG. 11, a ram head is located to the rightof the filling station, and this ram head is carried by a piston 166which is associated with an air cylinder 168. The stop 159 is so locatedas when lowered to properly position a filled mold assembly at thepressing station directly beneath the ram 165. Hence, when a filled mold132A is accurately located beneath the ram head 165, air under pressureis furnished to the cylinder 168 whereupon the ram head 165 is loweredand moves with force into the open upper end of the mold tray at thepressing station. In this manner, the material in the mold is compressedto the final desired thickness which in most instances will be Thisparticular dimension is the dimension at the thickest points of thetile. Thus, the area at the bottom of the tile form in the mold wherethe bars 136 and 137 are located will be less than /8" dimension, andhence the interior sections of the tile corresponding to the bars 136and 137 will be more dense than the adjacent sections corresponding tothe transverse bars of the screen 133 at the bottom of the moldcontaining the pressed tile form. This variation in thickness dimension,and consequently density, is shown in FIGS. 19 and 19A. Thus, the faceFF of the tile that was engaged by the ram head 165 is smooth since inthe present instance no design configuration is used in association withthe ram head. The back B of the tile, however, has narrow ribs RB wherethe tile form was pressed against the bars of the screen 133 and haswider depressed areas DA where the tile form in the mold was pressedagainst the bars 136 and 137 of the mold tray 132. It should be pointedout that the ram head face is of course oriented in a truly horizontalplane; hence, the face of the ram head will produce an accuratelyoriented face FF on the tile even though the screen at the bottom of themold might be slightly warped through over-use or over-heating.

Advantageously the ram is equipped with a removable presser shoe 165P,the lower face of which can be configured to impart the upper face ofthe mass in the tray whatever design is desired for the exposed face ofthe finished tile. By changing the shoe 1651, another design can beemployed. Once the ram head has been raised to clear a mold aftercompaction of the moist mix, a worker wipes the bottom face of the ramhead to clean loose material therefrom, or this can be done by anautomated wiper arm which is actuated once the ram head is raised.

Referring now to FIG. 16, the conveyor 150 moves the filled molds fromthe pressing station beneath a belt conveyor 170, the operation of whichwill be explained below. A stripper station is located on the right-handside of the belt 170 as viewed in FIG. 16 and it is here that eachscreen 133 and a pressed tile T supported thereby are removed from theassociated mold tray 132. The strippingniechanism comprises pins 172which are supported by lifter mechanism including a cross plate 175 inturn operated by an air piston and cylinder mechanism 176. The pins 172are so located as to move upwardly at the bottom four corners of themold trays 132 so that the upper ends of the stripper pins engage thefour corners of the screen 133 within the mold tray. During 23 thestripping operation, the conveyor 150 is of course stationary, andpreferably the connections are such that air is furnished to thecylinders for operating the ram head simultaneously with air underpressure being furnished to the stripper cylinder.

Once the tile T and its associated screen 133 have been raised upwardout of a mold tray as illustrated in FIG. 16, a worker lifts thisstripped assembly off the pins 172 and sets the same on a pair ofsupporting blocks 180 and 181 which are carried by the conveyor belt170, and this conveyor belt moves the tile and its supporting screen toa baking oven.

It was mentioned that the air cylinder which controls the ram 165 andthe air cylinder which controls the stripper pins 175 operate in unison,that is, when the ram 165 is down to compress, the pins 172 are up tostrip. Alternatively, when the presser ram is raised, the stripper pinsare lowered. This frees the conveyor 150 for its next movement toadvance a new filled mold to the pressing station and to advance acompressed but uncured tile to the stripper station. During this nextmovement of the conveyor, an emptied mold pan 132 at the stripperstation is turned about the sprockets 152, FIG. 16, to partake of thelower run of the conveyor 150, and this empty mold tray is movedgradually step-by-step toward the sprockets 151 at the mold loadingstation where it will eventually be provided with another screenavailable from the conveyor 155, FIG. 11. During the course of theirreturn movement from the stripper station to the mold loading station,the mold trays 132 are moved past a mold cleaning station 183, FIG. 16,where spray heads 184 or other fluid cleaning means are effective toremove loose matter from the side walls and bottom bars of the moldtrays. I

The pressed but unfired tile T removed at the stripper station andcarried by the screens 132, which now serve as pallets, are moved by theconveyor 170 toward an un loading table 185, FIG. 17, which is locatedat the input end of a long heat treating chamber generally indicated at190 in FIG. 17. Thus, as a leading one of the tiles T approaches theunloading table 185, this tile and four succeeding tiles are removed oneby one by a workman at the unloading table 185. In this connection, itwas explained above that the drawings illustrating the equipment andprocess steps are not drawn to scale for the most part, and it should beborne in mind that the long dimension of the table 185 is suflicient toenable at least five of the tiles to be set thereon in side-by-siderelation.

When an adequate number of tile have thus been removed from the conveyor170 and set on the table 185, these are then pushed as a set onto asprocket driven conveyor 191 which includes widely spaced conveyor bars191B enabling good heating from the bottom of the tile to be achievedWithin the heat treating chamber 190. The conveyor 191 moves slowlythrough the heat treating chamber. This speed in actual practice isapproximately two feet per minute, and it should be pointed out that theheat treating chamber alternates between what can be considered hot oractive oven banks 192 and interposed unheated or lull chambers 193.

A product of the kind produced under the present invention must be ofuniform characteristic throughout and dimensionally stable. The lattercharacteristic is achieved by the sodium silicate binder modified byurea or the like and which is cured, hardened and set up in the dryingchamber 190. Additionally, the open bottom nature of the supportingscreens 133 assure that there will be, as a practical consideration,every bit as efficient firing or heating of the tile from the bottom asfrom the top.

The tile is dried in three distinct states while passing through theheat treating chamber. In the first stage, the temperature of the tile(throughout its mass) is gradually raised to 210 F. within a period ofapproximately six minutes. The active ovens 192 are equipped with infra-24 red heaters, and the first stage occurs in bank one B1, FIG. 17, ofthe infra-red drier.

In the second stage, the tile temperature (throughout its mass) ismaintained between 190 F. and 210 F. by subjecting the tile to alternateperiods of radiant heat and lull periods wherein no direct heat isapplied to the tile; each of these periods (heat and lull) being ofapproximately six minutes duration. Stage two starts in the secondinfra-red bank B2 which is immediately adjacent to bank B1 andprogresses through the first lull period as in chamber 193, the thirdinfra-red bank B3, the second lull period, the fourth infra-red bank,the third lull period, and so on, and ends approximately half Waythrough the fifth infra-red bank, corresponding to forty-four minutes oftotal elapsed time of the drying cycle. The second stage isapproximately thirty-eight minutes in duration, and serves to evaporatethe free moisture in the tile.

The end of stage two and the start of stage three occurs when the tiletemperature begins to go above 210 F. indicating that free water hasbeen removed from the tile, and this takes place in the fifth infra-redbank at the forty-four minute point, as mentioned above. The tiletemperature reaches 260 F. at the end of the fifth infrared bank andgradually drops to 220 F. during the fourth lull period. The sixth andfinal infra-red bank causes the tile to reach 320 F., and at this pointthe tile is bone dry or very nearly so. Stage three serves to remove thewater of crystallization as required for bone dry condition and alsofurther activates the urea. Total time elapsed for all three stages isapproximately 60 minutes.

The infra-red oven, or banks as B1, referred to above are so constructedand designed that the tile is subjected to radiant energy on both topand bottom while the tile progresses through the drier on the conveyor191 in a horizontal plane. The conveyor 191 is designed to offer aminimum of obstruction to the radiant energy by widely spacing the bars191B, and the radiation is uniformly distributed over the conveyor areaand free from hot spots resulting in uniform heating of both sides ofthe tile. The source if radiant energy is a known standard industrialinfra-red lamp, employing a 4000 F. tungsten filament.

The intensity of the radiant energy directed at the tile isapproximately 500 watts per square foot on each side; i.e., top andbottom. An essential feature of the infrared banks is the use of agold-plated reflector in conjunction with the lamp. The reflector servesto project the energy uniformly, and since gold has a reflection factorof approximately 98% in the infra-red portion of the spectrum, theinitial component of radiant energy received by the reflector from thelamp as well as any energy that is reflected by the tile, is reflectedand ultimately absorbed by the tile.

Another essential feature of the drier is the method of ventilation.Room temperature air is used to cool the lamp bases and reflectors. Thisis accomplished without disturbing the air in the heated area by meansof double wall construction, whereby a separate chamber exists forcooling the lamps and reflectors. Thus, the lamps project throughopenings in a separate wall spaced above the tile. This wall isotherwise sealed off to afford a cooling chamber for the lamp equipmentand reflector backs. This room air is passed over the lamp bases andreflector backs and is heated to approximately F. and is then directedover the tiles passing through the radiant zone. The preheated airserves to carry oif the moisture released from the tile only and doesnot contribute to the heating effect, inasmuch as the air temperature orambient in the oven is lower than the tile temperature. However, bybeing preheated, the cooling effect of the air passing over the tile isminimized. The distribution of this air is uniform over the width of theconveyor 191 both top and bottom, so all tiles and on both sidesexperience the same condition.

The moisture laden air is forced out beyond the infrared banks into thelull or unheated areas 193 mentioned above and is carried off therein bymeans of exhaust ducts 195 and fans. The lull areas are essentiallyenclosed areas so constructed that the tile is not subjected to coldroom air but within a confined enclosure with the aforementionedcontrolled hot air movement.

Just before emerging from the last of chambers at the drying station,each set of tile may be subjected to a highly atomized cold water sprayto induce breaking the seal between each tile and its pallet screenfacilitating eventual separation of a tile from its pallet screen.

The completely cured acoustic tile emerge at the output end of the heattreating chamber generally defined by a downwardly sloped unloading tray197. As a series of five tile emerge from the output end of the heattreating chamber, a periodically reciprocating spray head 198 iseffective in one pass over the row of tile to spray the upwardlydisposed faces of the five tile with a pigment coating which in mostinstances will be an offwhite. The spray head 198 is of a known kind andis schematically illustrated in FIG. 17. This spray head is carried by asprocket driven chain 199. The motor for driving the drive sprocket isindicated at DM in FIG. 17, and it should be explained that theoperation of this motor is timed by a timing switch TS which in turn iscontrolled by a multi-lobed cam C, FIG. 17, which ro tates with one ofthe sprockets which is used to drive the conveyor 191 at its slow speedmentioned above. This cam is associated with the switch TS in such amanner that as each lobe on the cam passes the switch the latter isactuated to energize the motor which drives the chain 199 which carriesthe spray head 198. Limit switches (not shown) are located in positionto be actuated by the spray head as it reaches its end position afterone pass over a set of tile, and when a limit switch is actuated at theend of travel of the spray head, circuit to the drive motor for thechain 199 is interrupted, breaking the drive to the chain 199.Mechanical means (not shown) are eflective at the end of one pass of thespray head to uncouple the spray head from the run of the chain 199which carries the spray head to its end position and effective at thesame time to couple the spray head to the other run of the chain. Thus,assuming the chain 199 to be driven clockwise as viewed in FIG. 17, thelower run of the chain, when coupled to the spray head, will carry thespray head away from the observer while the upper run of the chain, whencoupled to the spray head, will carry the latter toward the observer.These two passes account for the spraying of ten tile, that is a firstrow of five tile emerging from the heat treating chamber, and then asecond row next emerging from the heat treating chamber. This of courseis repeated as long as there are tile emerging from the heat treatingchamber, all passes of the spray head occurring at intervals timed bythe cam C which of course is configured to cause actuation of the timingswitch TS as each set of tile reaches position beneath the spray head198.

As the tile and their supporting pallets 132 reach the top edge of theinclined plate 197, the pallet screens which carry the tile slide downthe plate 197 and on to the rollers of an inclined roller-type conveyor200. Workmen at this point remove from the screens the individual tileand stack the same on a receiving table 201, although such removal canbe performed automatically if desired by vacuum cups on a lifter head.The empty screens are then pushed along the conveyor 200 and travel downan inclined section 202 into and through a cooling chamber 205 whichcommunicates with a stack 206 which in turn is provided with a draft fanwhich causes a cooling draft to be created within the cooling chamber205 enabling the individual screens moving through the cooling chamber205 to be cooled down.

As the cooled screens 132 emerge from the cooling chamber 205, these arepicked up by a driven chain (not shown) disposed within the rollerconveyor 200, and this chain is effective to move each of the screensfirst beneath a rotating wire brush 210 which is effective to scrapetile flecks or residue from the screens. The chain operating in thetrough of the roller conveyor 200 is next effective to advance thescreens beneath a cleaning roller 212 which wipes the tops of thescreens 132 with a cleaning solvent and a releasing agent, and thescreens then move back to the mold loading station along the conveyor155. It should here be mentioned that advantageously the spray head forthe mold trays is adopted to spray a release agent and that when thebottom face of the ram head is wiped clean it is also to be wiped with arelease agent.

Referring to FIGS. 18 and 19, there is illustrated, respectively, thefront face FF and back B of an acoustical tile as it emerges from theheat treating chamber. The face FF is the one that will be exposed wheninstalled as an aspect of interior decoration, and unevenness of theback of the tile is of minor concern. In most instances, the face FFwill be fiat and uniform, but if desired this face can be a designimparted thereto by appropriate substitution of a design plate on theram head. The back of the tile as shown in FIG. 19 is extensivelyribbed. Thus, the back B of the tile has a raised rib R which is ofuniform dimension about the entire periphery of the back of the tile,and this rib corresponds substantially to the extents of the side endand bars 141148-149 of the screen in the mold. The back of the tile hasa center rib RC which corresponds to the transverse bar 142 of thescreen which, as mentioned above, fits in the channel in the bottom ofthe mold tray defined by the ties T, the top plane of the bar 142 lyingbelow the upper faces of the bars 136 and 137 at the bottom of the moldtray. The back of the tile also has parallel raised ribs RB separated bydepressions D, and these depressions D are the result of the mold traybars 136 and 137 projecting above the bars 145 and 146 of the screen asclearly shown in FIG. 15.

To facilitate installation, the tile are next moved to what can beconsidered a milling station where the edges of the tile are kerfed andbackcut. Additionally, the tile may be trimmed by abrading discs orwheels operative on the upper faces of the tiles. The essential elementsof the milling station are diagrammed in FIG. 20. Thus, the millingstation includes two feed belts 210 and 212 arranged at right angles onerelative to another. To facilitate an understanding of the sequence ofthe operations at the milling station, six tiles T0 to T5 areillustrated in FIG. 20 in various stages insofar as the operationsperformed thereon are concerned. The tile T0 represents a completelyfinished tile ready to be packaged and shipped to the customer, whereastile T5 represents a tile as it was received from the firing chamber.The first operations on the tile at the milling station are performed onthe tile carried by the belt 210, and lugs or bars (not shown) aremounted on the belt 210 to carry the tile along toward the observer asviewed in FIG. 20. Moreover, the tile are firmly held down on the upperbase of the belt 210 by resilient rollers (not shown). The firstoperation performed at the milling station is to kerf two side edges ofa tile as T5, and this operation is performed by a pair of kerfingcutters 214 and 215 that are located at opposite sides of the belt 210in position to cut into the left and right hand sides of the tile T5 asviewed in FIG. 20. Thus, as the belt 210 is effective to advance thetile T5 past the kerfing cutters or discs 214 and 215, these cut intothe left and right hand side edges of the tile T5 for a predetermineddepth, and this produces kerfs or slots KE1 and KE2 which areillustrated in FIG. 20 as provided in the tile T4 which was previouslyadvanced past the kerfing discs 214 and 215. These kerfs or slots areapproximately at the center line of the side edges of the tile, and itshould be explained

